Stock car racers and other racing vehicles have bodies without side windows and frequently without doors. The drivers enter these vehicles by climbing through a window opening. A roll bar cage is provided inside the body shell to keep the body shell from collapsing in on a driver in the event of a collision or roll-over.
Seat belts came into use a number of years ago to hold a driver in his seat inside the roll bar cage. In 1964, Joe Weatherly's stock car hit a retaining wall on the driver's side. The seat belt allowed the upper part of Weatherly's body to be thrown around and his head, shoulder, and left arm were forced outside the roll bar frame and through the window opening. His head hit the retaining wall and he was killed. As a result of Joe Weatherly's death, window nets were introduced to keep a driver's left arm, left shoulder and head within an area defined by the roll bar cage.
The window nets that are used today are attached to the roll bar cage adjacent to the drivers left side. The function of window nets is to retain a driver's head, left shoulder, and left arm within the area defined by the roll bar cage in the event of a roll-over or side impact. The window nets are also to keep rocks, car parts, and other foreign objects from entering the space defined by the roll bar cage.
The governing bodies which sanction stockcar racers have established minimum test procedures and specifications for race car components, including window nets. The SFI Foundation, Inc. window net specification requires window nets to prevent pass through of a solid ball that is three inches in diameter. The specification further requires that window nets prevent the penetration of a bag that is ten inches in diameter, weighs one hundred seventy five pounds, and is dropped from a height of fifteen inches above window nets that are held in a horizontal position.
Two types of window nets are commonly used. They are string window nets and ribbon nets. String window nets have a plurality of spaced horizontal strings and a plurality of spaced vertical strings. Visibility through string window nets is good. However, string window nets do not have sufficient strength to pass impact tests. String window nets generally will not prevent the penetration of a ten inch diameter bag weighing one hundred seventy five pounds that is dropped from a vertical height of fifteen inches. String window nets could also be expected to fail if a driver's body hit the net relatively hard.
Ribbon nets are made from a plurality of horizontal and vertical straps that are stitched together. The straps, which are usually one inch nylon webbing, are stitched together on three and one-fourth inch centers. This spacing produces two and one-fourth inch square apertures. The one inch wide webbing reduces side visibility substantially. Some race car drivers contend that the driver should be looking forward and that drivers do not need to look to the side. Other drivers race without ribbon nets unless the race track management requires window nets because of the side visibility problem. Drivers of off-road vehicles often need the protection of window nets and the side visibility. The width of the one inch webbing used to make ribbon nets cannot be decreased. These window nets have to be double stitched and cross stitched at each point where the webbing crosses to pass impact tests. When ribbon nets are subject to the one hundred seventy five pound, fifteen inch drop test, the ten inch diameter bag tends to exert substantially all of the force on two or three horizontal straps and on two or three vertical straps. Unless the webbing is stitched together well, the stitching can fail and allow the bag to penetrate the ribbon net. It takes time to stitch the horizontal and vertical webs to each other at each place they cross. The stitching requirements increase the cost of the window nets.